1. Field of the Invention
The present invention relates to a machine for etching the edge of a wafer. More particularly, it relates to a machine which can effectively remove the Si-needles on the edge of a wafer.
2. Description of the Prior Art
In order to increase the yields in the DRAM (dynamic random access memory) manufacturing, global wafer lithography methods are widely applied. Although the yields can be increased in this manner, there remain some difficulties related to the deep trench process.
FIG. 1 illustrates, in cross section, the conventional deep trench process. Referring to FIG. 1, a silicon wafer is provided as a semiconductor substrate 10. Then, the silicon dioxide layer 12, the silicon nitride layer 14 and the boron glass layer (not shown) are sequentially formed on the substrate 10. Each of the silicon dioxide layer 12, the silicon nitride layer 14 and the boron glass layer is called a hard mask layer. An anisotropic etching is performed to etch the boron glass layer, the silicon nitride layer 14, the silicon dioxide layer 12 and the substrate 10 to a certain depth to form deep trenches 15. The photoresist layer and the boron layer are removed, while the silicon nitride layer 14, the silicon dioxide layer 12 and a portion of the substrate 10 are left to form the Si-needles 16.
As global wafer lithography is used, Si-needles 16 are distributed across the whole wafer. When a clamp manipulator is used to transport the wafer, it grips the edge of the wafer and contacts the Si-needles, resulting in the breakage of a number of Si-needles, as illustrated in FIG. 2. The broken Si-needles are left on the wafer, increasing the probability of wafer damage and decreasing yields.
Therefore, in the prior art, the Si-needles on the edge of the frontside of the wafer are removed, as illustrated in FIG. 3. Thus, the edge of the wafer is smooth, and when the clamp manipulator is used to grip the edge of the wafer, Si-needles will not be broken.
The conventional method for removing the Si-needles on the edge of the frontside of the wafer is described as follows. Referring to FIG. 4, a photoresist layer is formed on the central part of the frontside of the substrate 10 shown in FIG. 1. Then, a dry etching is performed using the photoresist layer as a mask to etch the hard mask layer of the edge of the wafer, wherein the Si-needles are still left. Then, the substrate 10 is put on a single wafer machine and a backside etching is performed to remove the Si-needles on the edge of the frontside of the wafer.
FIGS. 5 through 7 illustrate the conventional single wafer etching machine, wherein FIG. 5 illustrates a top view, FIG. 6 illustrates the cross section I-Ixe2x80x2 of FIG. 5, and FIG. 7 illustrates the J-Jxe2x80x2 cross section of FIG. 5. The conventional single wafer etching machine comprises: a rotating holding plate 20 having a work platform, the work platform having a vacuum manipulator 21 (not shown), a gas spraying fillister 22, a plurality of holding pins 24, and an etching solution leading apparatus 26.
The vacuum manipulator 21 is used to grip and move the wafer 10 to a position between the work platform and the etching solution leading apparatus 26, wherein the frontside of the wafer faces towards the work platform and the backside of the wafer faces towards the etching solution leading apparatus 26.
The gas spraying fillister 22 is used to spray gas and thus maintain a certain distance between the frontside of the wafer and the work platform.
The holding pins 24 are used to fix and release the edge of the wafer 10 and rotate the wafer 10.
The etching solution leading apparatus 26 is set facing towards work platform and is used to lead etching solution to the back side of the wafer.
However, the method described above has the disadvantages described as follows: (1) it needs an additional photoresist layer, (2) due to the small space between the wafer and the work platform, the gas sprayed by the gas spraying fillister will generate a resistance, resulting in too little of the etching solution permeating-back on the frontside of the wafer thus, the removal of Si-needles on the edge of the wafer to be inadequate.
Accordingly, an object of the present invention is to provide a machine for etching the edge of a wafer having a frontside and a backside. The machine according to the present invention comprises: a rotating holding plate, an etching solution leading apparatus and at least one vacuum manipulator.
The rotational speed of the rotating holding plate is between 150 and 300 rpm. The rotating holding plate has a work platform. The work platform has a first fillister for spraying gas, a plurality of holding pins and an etching solution permeating-back fillister. The gas sprayed from the first fillister is used to maintain a certain distance between the frontside of the wafer and the work platform. Preferably, the gas is nitrogen. The holding pins are used for fixing and releasing the edge of the wafer and rotating the wafer. Preferably, there are six holding pins. The holding pins can be cylindrical-shaped and distributed equally around the work platform.
A second fillister is set around the periphery of the first fillister facing the edge of the frontside of the wafer. By reducing the pressure of the sprayed gas at the edge of the frontside of the wafer, the second fillister allows etching solution to easily permeate to the edge of the frontside of the wafer.
The etching solution leading apparatus is set facing towards the work platform and is used to lead etching solution to the backside of the wafer.
The vacuum manipulator is used to grip and move the wafer to a position between the work platform and the etching solution leading apparatus, wherein the frontside of the wafer faces towards the work platform and the backside of the wafer faces towards the etching solution leading apparatus.
Moreover, another objective of the present invention is to provide a method of etching the edge of a wafer having a frontside and a backside with a single wafer etching machine having a work platform with a first fillister and a second fillister set around the periphery of the first fillister, an etching solution leading apparatus, and a plurality of holding pins. The first step of the method for etching the edge of a wafer comprises spraying the gas from the first gas fillister. The wafer to be etched is then disposed on the work platform of the rotating holding plate, wherein the frontside of the wafer faces towards the work platform and the backside of the wafer faces towards the etching solution leading apparatus. Next, the gas sprayed on the frontside of the wafer maintains a certain distance between the frontside of the wafer and the work platform. The holding pins are contacted with the wafer, fixing the wafer such that the wafer can be rotated by the holding plate. Etching solution is lead from the etching solution leading apparatus to the backside of the wafer, such that the etching solution gradually diffuses to the edge of the backside of the wafer, and then permeates around to the edge of the frontside of the wafer, thereby etching the Si-needles at the edge of the frontside of the wafer. The wafer is released briefly by the holding pins and then gripped again, such that the edge of the wafer originally gripped by the holding pins is also etched.
Since the second fillister set around the periphery of the first fillister effectively reduces the gas pressure between the wafer and the workplatform in the area facing the edge of the frontside of the wafer, the etching solution easily permeates to the edge of the frontside of the wafer. Therefore, the photoresist is not necessary.